Adaptive bit swapping method and device for discrete multitone system

Abstract

Adaptive bit swapping method and device are provided. The method includes the steps of (a) initializing the DMT system to transmit the data via the channel in a steady state; (b) selecting a frame having an inserted sync block from a frame structure of the transmitted data; (c) calculating the signal-to-noise ratios (SNRs) of respective sub-channels of the selected frame; (d) calculating first difference value between the present representative SNRs calculated in step (c) and the previous representative SNRs of each sub-channel; (e) selecting a maximum value and minimum value among the first difference values of the respective sub-channels; (f) obtaining the second difference value between the maximum value and the minimum value; (g) determining whether the second difference value is equal to or greater than the predetermined threshold value; and (h) correcting bit and power assigning tables of a transmitter and a receiver if the second difference value is greater than or equal to the threshold value. In addition, the bit and power assigning tables can be accurately corrected since bits and power are swapped using an actually measured SNR.

What is claimed is: 
     
       1. An adaptive bit swapping method in a discrete multitone (DMT) system for an asymmetric digital subscriber line (ADSL) which has a transmitter for encoding and converting data to be transmitted via a channel, and a receiver for restoring the transmitted data to the original form by conversion and decoding, said method comprising the steps of: (a) initializing said DMT system to transmit said data via said channel in a steady state;   (b) selecting a frame having an inserted sync block from a frame structure of said transmitted data;   (c) calculating the signal-to-noise ratios (SNRs) of respective sub-channels of the selected frame;   (d) calculating first difference value between the present representative SNRs calculated in step (c) and the previous representative SNRs of each sub-channel;   (e) selecting a maximum value and minimum value among the first difference values of said respective sub-channels;   (f) obtaining the second difference value between said maximum value and said minimum value;   (g) determining whether said second difference value is equal to or greater than the predetermined threshold value; and   (h) correcting bit and power assigning tables of a transmitter and a receiver if said second difference value is greater than or equal to said threshold value.   
     
     
       2. An adaptive bit swapping method as claimed in claim 1, wherein said step (a) comprises the steps of: establishing the initial bits and power values of said DMT system; and   starting a transmission of data in a steady state of said DMT system.   
     
     
       3. An adaptive bit swapping method as claimed in claim 1, wherein said step (c) comprises the steps of; measuring the signal power spectrum density (PSD) of each sub-channel by a deterministic least sequence (DLS) method;   measuring a noise PSD of each sub-channel by a Welch method; and   calculating the SNR of each sub-channel from said measured signal PSD and said noise PSD.   
     
     
       4. An adaptive bit swapping method as claimed in claim 1, wherein said steps (b) and (c) are repeatedly performed by a predetermined times, and representative SNR value of each sub-channel are calculated making use of said SNRs if a predetermined number of SNRs are obtained for each sub-channel. 
     
     
       5. An adaptive bit swapping method as claimed in claim 4, wherein said step (c) comprises the step of; feeding the procedure back to said step (b), if said predetermined number of SNRs of each sub-channel are not obtained.   
     
     
       6. An adaptive bit swapping method as claimed in claim 1, wherein said step (g) comprises the step of; feeding the procedure back to said step (b), if said second difference value is not greater than or equal to said predetermined threshold value.   
     
     
       7. An adaptive bit swapping device functioning as a receiver for restoring the transmitted data to the original form by conversion and decoding, said device being included in a discrete multitone (DMT) system for an asymmetric digital subscriber line (ADSL) which has a transmitter for encoding and converting data to be transmitted via a channel, said device comprising: A/D converting means for converting the analogue data signal received via said channel into a digital signal;   time-domain equalizing means for receiving said digital signal and reducing a guard band used to remove an interblock interference;   fast-Fourier transforming means for receiving the output of said time-domain equalizing means and demodulating said data signal modulated in said transmitter;   frequency-domain equalizing means for receiving the output of said fast Fourier transforming means and compensating for a phase error of each sub-channel;   SNR measuring means for obtaining the representative SNRs of respective sub-channels from the output of said A/D converting means using a frame having an inserted sync symbol from a frame structure of transmitted data, calculating first difference value between the previous representative SNR and present representative SNR for each sub-channel, comparing a threshold value with second difference between maximum and minimum value of said first difference values and outputting to a transmitter and a receiver the signal used for correcting a bit allocation table according to the compared result; and   decoding means for receiving the outputs of said SNR measuring means and said frequency-domain equalizing means, resetting a slice value, and decoding the reset slice value.   
     
     
       8. An adaptive bit swapping device functioning as a receiver for restoring the transmitted data to the original form by conversion and decoding, said device being included in a discrete multitone (DMT) system for an asymmetric digital subscriber line (ADSL) which has a transmitter for encoding and converting data to be transmitted via a channel, said device comprising: A/D converting means for converting the analogue data signal received via said channel into a digital signal;   time-domain equalizing means for receiving said digital signal and reducing a guard band used to remove an interblock interference;   fast-Fourier transforming means for receiving the output of said time-domain equalizing means and demodulating the data signal modulated in said transmitter;   frequency-domain equalizing means for receiving the output of said fast Fourier transforming means and compensating for a phase error of each sub-channel;   SNR measuring means for selecting a frame having an inserted sync block from a frame structure of said transmitted data, calculating the signal-to-noise ratios (SNRs) of respective sub-channels of the selected frame, calculating first difference value between the present representative SNRs calculated above and the previous representative SNRs of each sub-channel, selecting a maximum value and minimum value among the first difference values of said respective sub-channels, obtaining the second difference value between said maximum value and said minimum value, determining whether said second difference value is equal to or greater than a predetermined threshold value and outputting to a transmitter and a receiver the signal used for correcting bit and power assigning tables of a transmitter and a receiver; and   decoding means for receiving the outputs of said SNR measuring means and said frequency-domain equalizing means, resetting a slice value, and decoding said reset slice value.